1. Field of the Invention
This invention relates broadly to methods of chemically treating articles in solutions. In a preferred embodiment, this invention relates to uniformly dispersing ophthalmic lenses in a chemical treatment solution.
2. Description of the Related Art
Hydrophilic contact lenses may be treated with a variety of solutions in a variety of ways to modify the lens properties. For example, contact lenses are typically subjected to extraction processes during the manufacture of the lens in order to remove undesirable solvents originating from the polymerization or molding steps. A contact lens may also be exposed to a treatment solution containing a reactive dye, in order to impart ultraviolet (UV) light absorbing properties or visible light absorbing properties to the lens. Another example of contact lens treatment involves exposure of the lens to a monomer solution with graft polymerization being induced to alter the surface properties of the lens.
Conventional means of tinting contact lenses may be divided into bath processes and printing processes. In the printing process, a silicone rubber printing head conveys a reactive dye to the surface of the lens. In the bath process, the lens, or a portion of the lens, is immersed in a solution containing a reactive dye.
In order to efficiently and economically tint lenses, one may treat many lenses at one time by placing the lenses in a container holding the reactive dye solution in a static state. A problem with this method of treatment is that the lenses may cup or coalesce (i.e., two or more lenses may adhere to one another), thereby promoting localized dye concentration gradients. Also, the lens may rest against the container, again resulting in the lens experiencing different dye concentrations across the surface. These concentration gradients result in non-uniform tinting of the lens, sometimes causing serious discolorations in the lens-surface. Further, lens coalescing generates problems with separating the lenses because of the strong adhesion between lenses.
The lenses may also be treated by placing each lens in a separate well or compartment within a tray having numerous wells. Typically, the lenses are placed concave-side up in wells which are adapted to hold the lens (i.e., the wells are typically concave-shaped to match the convex surface of the lenses). Such a tray holding numerous lenses may be immersed in a tinting or monomer grafting solution in order to efficiently treat many lenses at once. Although this technique eliminates the coalescing problems, there remain problems associated with the lenses resting against the tray wells. For example, an extended contact period of the lens with the tray causes concentration gradients, resulting in lenses which are non-uniformly tinted or non-uniformly surface-modified.
Thus, there is a need for a method of exposing contact lenses to a treatment solution in an efficient, economical, and uniform manner. There also remains a need for an apparatus which simultaneously contacts numerous lenses with a treatment solution in a uniform manner.